The batsman is expected to still line up in the third Ashes Test on Thursday at Old Trafford, but a key player being unable to train two days out from a must win match is more unwelcome news for Australia who are battling to keep the series alive.
Smith made 102 not out in Australia's Tour match against Sussex in Hove, but didn't bowl at all in the three day affair.
It's unknown when Smith picked up the back problem, but he has a history of trouble in that area.
The 24-year-old was a key bowling option in the second Test at Lord's, and on an Old Trafford deck that's expected to turn, Australia will be desperate for Smith to contribute the odd over with his leg spin.
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Australian captain Michael Clarke took the tour match off to rest his troublesome back but he trained on Tuesday and is fit to play.
Darren Lehmann said Clarke should be fit to bowl if needed.
David Warner batted in the nets in Manchester after returning on Monday afternoon from his stint with Australia A in Africa.
If selected, Warner could provide another spinning option for Clarke.
Australian opener Chris Rogers says Smith wasn't in too much pain and expects to play.
"Not really. I think it's (Smith's back) just a bit restrictive so hopefully it's not a big issue," Rogers said."I think he's doing ok. I think he might have tweaked it a little bit yesterday but talking to him he said he's improved a bit so hopefully he'll be right to train tomorrow and good to go on the first day."